1. Field of the Invention
This invention is concerned with novel extreme pressure additives and with lubricant compositions containing said additives.
2. Background of the Invention
Lubricants are widely used to reduce the friction between surfaces of moving parts and thereby reduce the wear and prevent damage to the parts. Most of the lubricants are comprised principally of a base stock which is generally a relatively high molecular weight hydrocarbon. In applications where the amount of pressure applied to the moving part is quite high, lubricants which are comprised of only hydrocarbon base stock tend to fail and the parts in contact are damaged.
It is well known to add materials to increase the high pressure performance of lubricants. These materials are generally referred to as extreme pressure additives. The most commonly used extreme pressure additives are sulfurized unsaturated fatty materials such as sulfurized sperm whale oil. It is believed that in the sulfurization process the sulfur adds to the double bonds to form monosulfides and disulfides.
One of the problems encountered in the manufacture of sulfurized extreme pressure additives is that raw materials used in certain of these additives vary considerably in price and availability. A typical example of such a raw material is sperm whale oil. The number of sperm whales harvested each year is decreasing. Accordingly, with the decrease in the supply, the cost has markedly increased. Furthermore, since there is a possibility that sperm whales may become extinct due to overkill, the sperm whale has been classified as an endangered species. To prevent continued hunting of the sperm whale it has been suggested that the importation of sperm whale oil be prohibited and thereby thus eliminate the market.
With the exception of sperm whale oil other common fatty materials have not proven to be completely satisfactory for use in extreme pressure additives. While sperm whale oil is a special case with regard to availability, other oils and fats used in extreme pressure lubricants can vary considerably in price, availability and quality from time to time. A poor crop of corn, for example, can markedly increase the price of corn oil because of the resulting limited supplies.
One of the principal problems with most extreme pressure additives is one of compatability with the lubricant base stock. Many fatty materials when sulfurized do not form clear solutions with the lubricant base stock. The resulting mixtures are hazy to definitely cloudy and even, in certain cases, the additives will precipitate from the mixtures. Lubricants which are sold for use in high pressure applications must be clear, in order to be commercially acceptable. The resason for this is obvious in that the lubricants will be subject to extreme conditions in use and accordingly it is felt that a hazy mixture under normal conditions would be more likely to break down under extreme pressure conditions.
A further problem is that certain starting fatty materials are highly reactive in the sulfurizing process. As a result, there is believed to be an excessive amount of sulfur cross-linking which adversely effects both the solubility and extreme pressure characteristics of the additives formed from these materials.
The most important factor to be considered in the selection of any extreme pressure additive is the effect it will have on preventing damage to the surfaces which are in sliding contact. The effect of extreme pressure on a lubricant can be seen by the fact that the SAE load-carrying capacity of a typical naphthenic base oil without an extreme pressure additive is only about 25 pounds. However, the addition of 4.5% of sulfurized sperm whale oil increases the load carrying capacity from 25 pounds to 312 pounds, as reported in Table 1 of the paper "Influence of Chemical Structure in Sulfurized Fats on Antiwear Behavior" by A. Dorinson, American Society of Lubrication Engineers Preprint 70LC-8.